RULERS OF THE ANCIENT SEAS 53 



of Africa and Asia, especially adapted to a 

 roving, predatory life by their powerful tails 

 and paddle-shaped feet. Their cup-and-ball 

 vertebrae indicate great flexibility of the body, 

 their sharp teeth denote ability to capture slip- 

 pery prey, and the structure of the lower jaw 

 shows that they probably ate in a hurry and 

 swallowed their food entire, or bolted it in 

 great chunks. The jaws of all reptiles are 

 made up of a number of pieces, but these are 

 usually so spliced together that each half of the 

 jaw is one inflexible, or nearly inflexible, mass 

 of bone. In snakes, which swallow their prey 

 entire, the difficulty of swallowing animals 

 greater in diameter than themselves is sur- 

 mounted by having the two halves of the lowei 

 jaw loosely joined at the free ends, so that 

 these may spread wide apart and thus increase 

 the gape of the mouth. This is also helped by 

 the manner in which the jaw is joined to the 

 head. The pelican solves the problem by the 

 length of his mandibles, this allowing so much 

 spring that when open they bow apart to 

 form a nice little landing net. In the Mosa- 

 saurs, as in the cormorants, among birds, there 



